The present invention relates to television systems and more particularly to television transmitting and receiving systems involving codified signals of the type useful for subscription television use. While the present system will be described in the environment of conventional television broadcasting and home television reception, it likewise is applicable to satellite television systems, cable television systems and the like.
Numerous systems and approaches to subscription television and other forms of scrambled video have been proposed, tested and used. Some systems use a relatively sophisticated decoder for unscrambling the television signals and which does not require any form of decoding card, or hardwire control from a remote facility, for setting the decoder to properly perform its function. Some of these systems are addressable over the air to enable different tier programming. While these forms of systems do not require any card control or hardwire connection (e.g., a telephone line connection for addressing the decoder), they lack high security inasmuch as the electronic system of the decoder can readily be copied. Other systems have been proposed which involve complicated over the air addressing schemes to address and set each subscriber's decoder. These are subject to the problem of nonreceipt or improper receipt of the addressing code and the attendant maintainance problems, such as described in U.S. Pat. No. 4,081,832. Numerous other systems which have been proposed are relatively complicated or require hardwire addressing schemes, such as noted in U.S. Pat. No. 3,069,492. Other examples of prior systems are discussed in U.S. Pat. No. 3,801,732 which describes a scrambled television system involving the use of a punched card and in which both video and sychronizing information are altered in a predetermined manner, and U.S. Pat. No. 3,736,369 and No. 3,890,461 which describe ticket or card operated subscription television systems.
It has been the objective of workers in this field to provide a codification or scrambling system which is secure and difficult to pirate, provide a relatively inexpensive system inasmuch as a major use will be by individual home subscribers thereby necessitating production of a substantial number of decoders, provide a system which is easy to use and which enables a number of tiers of programming to be provided, and to provide a system which also includes codification of audio but which still can enable good audio reception and barker information.